The present invention relates to a control device and control method for a hybrid vehicle propelled with at least one of drive power outputs of an internal combustion engine and a motor via a stepped power transmission.
An example of a related art hybrid vehicle is disclosed in U.S. patent application Publication Laid-open No. 2002-0062183A1. With such a related art structure, the hybrid vehicle includes an internal combustion engine, a motor, an electric storage device and a power transmission to form a so-called hybrid vehicle in which at least one of drive power outputs of the internal combustion engine and the motor is transmitted via the power transmission to an output shaft thereof. In such a hybrid vehicle, a running mode and an operating point of a unit (the internal combustion engine, the motor and the power transmission) are determined such that the running efficiency (indicative of a proportion of a fuel flow rate, in terms of a drive power rate required for driving the vehicle, required for providing such power rate) is equal to a target value.
In such a concept, a target running efficiency is determined such that the higher the SOC value indicative of a remaining charged state of the electric storage device, the higher will be the target running efficiency. This results in a condition where the unit operating point is controlled such that as the SOC value remains at a high level, the electric storage device is charged only at the high running efficiency whereas when the SOC value remains at the low level, charging of the electric storage device is effectuated even at the low running efficiency. For this reason, it is possible to execute a control so as to permit the SOC value to be varied within an available range and to properly provide a given physical value, such as an exhaust gas flow rate and fuel consumption rate, related to the internal combustion engine.
In the related art practice set forth above, operating points of the internal combustion engine to be used during a travel of the vehicle are compared between a case in which the power transmission includes an infinitely variable power transmission, such as a CVT, and a case in which the power transmission includes a stepped power transmission.
An example of a structure, which employs the infinitely variable power transmission, is shown in FIG. 1 in which a hybrid vehicle is structured with an internal combustion engine 21, a clutch 22, a motor 23, the infinitely variable power transmission 24, a gear reduction unit 25, a gear differential 26 and drive wheels 27. With such a vehicle, the presence of the infinitely variable power transmission 24 located for transmitting a drive power output of either one of the internal combustion engine 21 and the motor 23 or drive power outputs of both the engine and the motor to the drive wheels 27 enables an operating point of the internal combustion engine during running of the vehicle to be freely selected from an operating point tracing an equivalent power rate line that satisfies a drive power rate. Such a hybrid vehicle takes an advantage of the freedom of selecting the operating point while an attempt is made to control the operating point of the internal combustion engine to trace an xcex1 line for thereby providing an improved fuel consumption.
In contrast, with an alternative structure in which the infinitely variable power transmission 24 (inclusive of a hydraulic device 28, a motor 29 and an inverter 31) of FIG. 1 is replaced with the stepped power transmission, since the operating point of the internal combustion engine is determined on the basis of a rotational speed of the internal combustion engine during the running condition, a vehicle speed and respective gear shift stages, the operating point of the internal combustion engine is forced to be selected from an intersecting point between the equivalent power rate line, that satisfies the drive power rate, and the rotational speed that can be taken out for each gear shift stage. FIG. 2 shows the operating points, encircled with ◯, of the internal combustion engine and the stepped power transmission that satisfy the drive power rate shown in a dotted line. Also shown by a thin solid line in FIG. 2 is an equivalent running efficiency curve. In order for the improved fuel consumption to be provided with such a vehicle, the gear shift stage comes to be selected such that the operating point of the internal combustion engine becomes the high efficiency, with the freedom in selecting the operating point becoming smaller than that of the infinitely variable power transmission. Further, in an event that the internal combustion engine provides the power rate beyond the drive power rate with an excess of the power rate causing an electric power output to be produced and charged into the electric storage device, since the rotational speed is similarly determined with the vehicle speed and only the resulting torque output is regulated to increase the power rate of the internal combustion engine, the freedom of selecting the operating point becomes small. Thick solid lines in FIG. 2 show the operating points taken out for respective gear shift stages.
Thus, since no consideration is made for a difference in the operating points of the internal combustion engine in the case of the power transmission composed of the infinity variable type/stepped type structures, an issue arises in that the related art practice can not sufficiently comply with a requirement for selecting the gear shift stage and calculating the unit operating point.
Further, when calculating the unit operating point that forms the target running efficiency, a difficulty is encountered in that the gear shift happens to occur even in the absence of variation in drive power demanded by a driver and the gear shift doe not occur from a high speed gear ratio to a low speed gear ratio or from the low speed gear ratio to the high speed gear ratio, with a resultant situation to give a different feeling touch to the driver.
With the above view in mind, the present invention has an object to provide a control device and control method for a hybrid vehicle in which at least one of drive power outputs of an internal combustion engine and a motor is connected through a stepped power transmission to an output shaft thereof and which enables a target unit operating point, satisfying a target running efficiency, to be realized for effectively eliminating the amount of fuel required for entire running and the amount of exhaust ingredients to be limited.
It is another object of the present invention to provide a control device and control method for a hybrid vehicle in which at least one of drive power outputs of an internal combustion engine and a motor is connected through a stepped power transmission to an output shaft thereof and which is able to alleviate a different feeling touch to be given to a driver due to a variation in a rotational speed of the internal combustion engine during a gear shift.
To achieve the above objects, according to a first aspect of the present invention, there is provided a control device for a hybrid vehicle, including a unit having an internal combustion engine, a motor, a stepped power transmission and an electric storage device adapted to supply electric power output to the motor, wherein at least one of power outputs of the internal combustion engine and the motor is transmitted through the stepped power transmission to an output shaft thereof, the control device comprising a state of charge detecting section detecting an SOC value indicative of a remaining charged capacity of the electric storage device, a target running efficiency calculating section calculating a target value of a running efficiency, indicative of a proportion of a given physical quantity, in terms of a drive power rate required for driving the vehicle, in such a manner that the higher the SOC value, the small will be the target value to be calculated, a target unit operating point calculating section calculating a target value of a unit operating point, that forms the target running efficiency, from among operating points of the unit which cause the drive power rate provided by the internal combustion engine to be utilized at the running efficiency with the maximum efficiency, and a target unit operating point actualizing section controlling the unit such that the unit is operated at the target unit operating point.
According the first aspect of the present invention, since the control device controls the hybrid vehicle, including the unit having the internal combustion engine, the motor, the stepped power transmission and the electric storage device adapted to supply electric power output to the motor, with the at least one of the power outputs of the internal combustion engine and the motor being transmitted through the stepped power transmission to the output shaft thereof using the state of charge detecting section detecting the SOC value indicative of the remaining charged capacity of the electric storage device, the target running efficiency calculating section calculating the target value of the running efficiency, indicative of the proportion of the given physical quantity, in terms of the drive power rate required for driving the vehicle, in such a manner that the higher the SOC value, the small will be the target value to be calculated, the target unit operating point calculating section calculating the target value of the unit operating point, that forms the target running efficiency, from among operating points of the unit which cause the drive power rate provided by the internal combustion engine to be utilized at the running efficiency with the maximum efficiency, and the target unit operating point actualizing section controlling the unit such that the unit is operated at the target unit operating point, it is possible to optimize the proportion of the physical quantity in terms of the drive power rate required for driving the vehicle.
Thus, the present invention concerns an important advantage of a capability for controlling the hybrid vehicle at the highest unit operating point to satisfies the target running efficiency, resulting in an improvement over the running efficiency. This causes the amount of fuel consumption required for an entire running stroke of the vehicle to be effectively decreased.
Another advantage resides in that due to the capability of controlling the hybrid vehicle at the highest unit operating point, the internal combustion engine is enabled to operate at the highest efficiency throughout a whole running state of the vehicle while remarkably eliminating emission of harmful compounds such as CO, HC and Nox.
The present invention further concerns an important advantage of a capability of activating the unit, inclusive of the internal combustion engine, the motor and the stepped power transmission, at the target running efficiency which varies such that the larger the SOC value, the smaller will be the target running efficiency whereby excessive charging or discharging of the electric storage device can be alleviated to preclude the same from being seriously deteriorated.
According to a second aspect of the present invention, there is provided a control method for a hybrid vehicle, including a unit having an internal combustion engine, a motor, a stepped power transmission and an electric storage device adapted to supply electric power output to the motor, wherein at least one of power outputs of the internal combustion engine and the motor is transmitted through the stepped power transmission to an output shaft thereof, the control method comprising detecting an SOC value indicative of a remaining charged capacity of the electric storage device, calculating a target value of a running efficiency, indicative of a proportion of a given physical quantity in terms of a drive power rate required for driving the vehicle in such a manner that the higher the SOC value, the small will be the target value to be calculated, calculating a target value of a unit operating point, that forms the target running efficiency, from among operating points of the unit which cause a power rate provided by the internal combustion engine to be utilized at the running efficiency with the maximum efficiency, and controlling the unit in a way to actualize operation of the unit at the target unit operating point.